@DOC Welcome to the forum!
Interesting indeed.
Hmm. I wonder how that could happen. It might be that one of them could be a replacement for an error on 777886 or 777885, which was set with the wrong number, in error.

Here's a serious rarity, an error on a replacement note
A printed fold, causing the date to appear on the back of the note when unfolded. I wonder if this replacement was itself replaced.

Here's an interesting note I came across recently. It is a Bank of Ireland Pound signed by Adams, which has been counter-signed by Chestnutt and Guthrie, who were both later signatories of the BoI notes (Chestnutt,1960s; and Guthrie, 1970s).

These 2 banknotes' dates are exactly 50 years apart! Interestingly enough, they're both in my own collection, and I only realized that the dates were special yesterday, when I was looking through my collection!

Here are a pair of Lady Lavery notes sold recently at the The Whytes Eclectic Collector 9/18 Auction. The 10 shillings and £1 notes are unremarkable apart from the fact that they are autographed by Dr. T.K. Whitaker, former Secretary of the Department of Finance and Governor of the Central Bank of Ireland. He was once voted Irishman of the 20th century. The pair of notes sold for a hammer price of 280 euro which is considerably more than their value without the signature.

Here are a pair of Lady Lavery notes sold recently at the The Whytes Eclectic Collector 9/18 Auction. The 10 shillings and £1 notes are unremarkable apart from the fact that they are autographed by Dr. T.K. Whitaker, former Secretary of the Department of Finance and Governor of the Central Bank of Ireland. He was once voted Irishman of the 20th century. The pair of notes sold for a hammer price of 280 euro which is considerably more than their value without the signature.